Subnet Mask

A mask used to determine what subnet an IP address belongs to. An IP address has two components, the network address and the host address.

A subnet mask separates the IP address into the network and host addresses.

For example

consider the IP address 150.215.017.009.
Assuming this is part of a Class B network, the first two numbers (150.215) represent the Class B network address,
the second two numbers (017.009) identify a particular host on this network.






A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address.

The result is the subnetwork address:

Subnet Mask    255.255.240.000 11111111.11111111.11110000.00000000

IP Address    150.215.017.009 10010110.11010111.00010001.00001001

Subnet Address 150.215.016.000 10010110.11010111.00010000.00000000